The present invention relates to a servocontrolled magnetic gripping device.
More specifically, the present invention relates to a magnetic gripping device particularly suitable for assembly on pneumatic manipulators, to which the following description refers purely by way of example.
As is known, on certain assembly lines, particularly large, heavy parts are handled manually with the aid of pneumatic manipulators for sequentially engaging the part, lifting it to a predetermined height, and then compensating the weight of the part itself so that it can subsequently be moved manually by the operator with a minimum amount of effort.
When handling parts made of ferromagnetic material, such as ferrous sheet metal, the free end of the pneumatic manipulator is normally fitted with a magnetic gripping device for selectively engaging and retaining the part using the magnetic field produced by the device itself.
With reference, for example, to patent WO-9965644, the magnetic gripping devices normally featured on medium-small-capacity pneumatic manipulators comprise an outer anchoring surface, which rests on the part to be gripped, and are normally defined by two magnetic cores mounted for rotation one inside the other, so that the inner magnetic core can be rotated manually, by a given angle about a given axis of rotation, between two distinct operating positions, in which the magnetic poles of the inner magnetic core face the magnetic poles of the outer magnetic core to eliminate or amplify the magnetic field produced by the latter at the outer anchoring surface.
The inner and outer magnetic cores are both made of ferromagnetic material and permanent magnets, and are so shaped that the operator can only switch from the first operating positionxe2x80x94in which the outer anchoring surface has substantially no magnetic fieldxe2x80x94to the second operating positionxe2x80x94in which the outer anchoring surface is crossed by a strong magnetic fieldxe2x80x94when the outer anchoring surface is positioned resting on a ferromagnetic part.
In other words, the inner and outer magnetic cores are so shaped that the force exerted by the operator on the lever controlling rotation of the inner magnetic core is particularly high when the outer anchoring surface does not rest on a ferromagnetic part, and, conversely, is relatively low when the outer anchoring surfaces does rest on a ferromagnetic part.
The main drawback of magnetic gripping devices of the above type is that of failing to provide any guarantee of retaining the ferromagnetic part once the inner magnetic core is rotated manually by the operator from the first to the second operating position.
In this type of gripping device, in fact, the maximum load, that can be lifted, depends predominantly on the distance or so-called xe2x80x9cgapxe2x80x9d created between the surface of the part for lifting and the outer anchoring surface of the gripping device by dirt on either one of the two surfaces.
Very frequently, in fact, owing to a thin film of oil, dust or paint between the two surfaces, the ferromagnetic part is suddenly released by the gripping device after it has been lifted and its weight compensated by the pneumatic manipulator. And since sudden variations in load produced by accidental release of the part cannot be compensated immediately by the pneumatic load-compensating system on the pneumatic manipulator, the arm of the manipulator rears uncontrollably and may strike the ceiling with considerable force.
Accidental release of the part also endangers the safety of the operator. In fact, not infrequently, the part drops directly on to the operator""s legs, thus causing serious injury.
It is an object of the present invention to provide a magnetic gripping device designed to eliminate the aforementioned drawbacks.
According to the present invention, there is provided a magnetic gripping device comprising a magnetic assembly defined by an outer magnetic core, and by an inner magnetic core mounted inside the outer magnetic core so as to rotate, about a given axis of rotation, between a first operating position, in which the inner magnetic core prevents the outer magnetic core from attaching magnetically to the surface of a generic part of ferromagnetic material, and a second operating position, in which the inner magnetic core allows the outer magnetic core to attach magnetically to the surface of said part; the gripping device being characterized by comprising torque-control actuating means, which, on command, rotate the inner magnetic core in such a manner as to set it selectively to the first or second operating position, while controlling the value of the twisting torque employed in doing so.